Transglutaminases are a group of calcium dependent enzymes that catalyze the crosslinking of proteins by promoting the formation of .epsilon.-(.gamma.-glutaminyl)lysine isopeptide bonds between protein-bound glutamine and lysine residues. These enzymes are believed to be widely distributed in nature, as the crosslinks are found in both prokaryotic and eukaryotic cells. Although different transglutaminases appear to be very similar in substrate specificity, several distinct forms of the enzymes have been identified. See generally, Folk, Ann. Rev. Biochem. 49:517-531 (1980).
Transglutaminase-mediated protein crosslinking reactions have been implicated in both normal and pathological processes in mammalian cells and tissues. The crosslink may act to maintain some forms of protein structure, such as in the terminal differentiation of epidermal cell layers and in other cellular architecture. An intracellular transglutaminase known as epidermal or Type I transglutaminase has been isolated and cloned from rabbit epithelial cells (Floyd and Jetten, Mol. Cell. Biol. 9:4846-4851 (1989)), and a transglutaminase has been isolated and cloned from guinea pig liver cells (Ikura et al., Biochem. 27:2898-2905 (1988)). Other transglutaminase activities have been described including hair follicle transglutaminase, keratinocyte transglutaminase, and prostate transglutaminase (Wilson et al., Fed. Proc. 38:1809 (1979)). Lee et al., Prep. Biochem. 16:321-335 (1986) have described the purification of a transglutaminase from human erythrocytes. These transglutaminases have been shown to be distinct from a plasma transglutaminase, Factor XIII, an enzyme whose primary function appears to be stabilizing fibrin clots. Factor XIII has also been purified, cloned, and sequenced. (Ichinose, et al., Biochem. 25:6900-6906 (1986), Takahashi, et al., Proc. Natl. Acad. Sci. U.S.A. 83:8018-8023 (1986)).
Transglutaminases have been employed for crosslinking purposes in a variety of fields. Certain microbial transglutaminases have found use in food technology to add texture to processed foods, particularly fish and cheese. Others have been used in enzyme-catalyzed fluorescent labeling of proteins, in the introduction of cleavable crosslinks, and in the solid-phase reversible removal of specific proteins from biological systems. Factor XIII preparations have been proposed for a variety of therapeutic uses, such as the treatment of subarachnoid hemorrhage and inflammatory bowel disease.
Presently, a plasma derived Factor XIII is available as a fibrin sealant, but, as with most plasma-derived products, carries an inherent risk of viral contamination. Further, Factor XIII and certain other transglutaminases are zymogens, requiring some form of activation to become catalytically active. And, as each transglutaminase has a restricted range of substrates, their activity may be limited in certain applications. Accordingly, what is needed in the art are methods for producing by recombinant means human transglutaminases. The present invention fulfills these and other related needs.